More from WebMD

June 9, 2010 -- Having too little vitamin D may not be due solely to diet or lack of sunlight, but may be due to your genes.

An international consortium of researchers and doctors has identified four gene variants that may play a role in vitamin D deficiency, a condition which may affect up to half of all healthy adults in the developed world. It can contribute to poor musculoskeletal health as well as potentially increase the risk of diabetes, cardiovascular disease, and certain types of common cancers.

Knowing who carries the gene variants could help doctors identify who is at risk for vitamin D deficiency and could potentially help reduce the risk of low vitamin D before the problem advances.

Researchers in the SUNLIGHT Consortium (Study of Underlying Genetic Determinants of Vitamin D and Highly Related Traits) analyzed data from 15 epidemiologic groups that included nearly 34,000 whites of European ancestry. The team looked at vitamin D concentration levels in the blood as well as genetics. Vitamin D insufficiency was defined as concentrations lower than 75 nmol/L (nanomoles per liter) or 50 nmol/L.

Three common gene variants -- including those involved with cholesterol, vitamin D metabolism, and transporting vitamin D throughout the body -- were associated with vitamin D deficiencies. The researchers found that the more of these variants an individual had, the greater the risk of having low vitamin D levels.

In fact, individuals who had inherited several of the gene variants and who fell in the highest quartile in the group had a two-and-a-half times increased risk of having a blood vitamin D concentration that was lower than 75 nmol/L when compared with those in the lowest quartile, who had fewer of these gene variants and were at a lower risk.

The findings will be published in The Lancet and were released online early.

Rethinking Treatment Strategy

The researchers say the results may make doctors rethink treatment strategies for improving patients' vitamin D deficiencies. However, they note that they only studied white populations, so it is unclear if these gene variants would be identified in other racial/ethnic groups.

"It's possible that these results could explain why some people respond well to vitamin D supplements and others don't, but that needs to be studied further since we didn't specifically examine response to supplementation," said Thomas Wang, MD, a consortium member and cardiologist at Massachusetts General Hospital in Boston, who co-authored the report. "We also need to investigate how genetic background can modify response to sunlight, whether these associations are seen in other populations, and if these gene variants have an impact in the chronic diseases that appear to be associated with vitamin D deficiency."

In an accompanying editorial published in The Lancet, Roger Bouillon, MD, from the Katholieke Universiteit in Leuven, Belgium, writes: "Today's results only partly explain the wide variability of vitamin D status, and whether these genetically based variations modify the health outcomes in vitamin D deficiency is not known. Therefore the battle against vitamin D deficiency will probably not be modified by these new findings. We need additional studies to explain the mechanisms underlying the pandemic of vitamin D deficiency and, above all, we need a strategy to correct this serious worldwide deficiency."

Vitamin D is essential for calcium absorption and bone health; it helps regulate immune function, among other roles. Vitamin D is naturally produced in the skin when you are outside exposed to ultraviolet light from the sun.

Foods that naturally contain vitamin D include fish (particularly salmon and tuna) shrimp, and eggs. Many foods are now fortified with vitamin D, including milk and other dairy products, to boost overall vitamin D intake. Taking a dietary supplement containing vitamin D is also a common way to maintain sufficient vitamin D levels.